Natural Draft Combustion Mixer

ABSTRACT

A natural draft combustion mixer in which the primary air intake is positioned downstream from the point of fuel introduction and also consists of a heat return port for orifice freeze protection that is located adjacent to the orifice, as well as a removable orifice holder for ease of access to the orifice during maintenance and set-up of a combustion system.

CROSS-REFERENCE TO RELATED APPLICATIONS

As per 35 USC §119(e), this application is related to the provisionalapplication filed on Nov. 27, 2012. Application No. 61/730,455(Confirmation Number: 5768)

STATEMENT REGARDING FEDERALLY SPONSERED RESEARCH OR DEVELOPMENT

Not Applicable

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND OF INVENTION

A natural draft combustion mixer is a device that is utilized inprocesses where heat is required and achieved by means of heat releasefrom the combustion reaction of fuel and air in a combustion chamber.The mixer is used to perform the mixing of the fuel and air to achieve amixture above the LEL (lower explosive limit) and below the UEL (upperexplosive limit). The primary air shutter is used to control the amountof air that is entering the mixer to attain the required combustionproperties. An orifice, of various sizes depending on capacityrequirements, is used to calculate the actual volume of fuel per unittime that passes through from a point of predetermined pressure to anarea of atmospheric pressure. It is also the point where the well knownphysics principle of high velocity creating a low pressure area is usedto cause atmospheric pressure to push air into the mixer or induce air.The mixture exits through a nozzle at which point the ignition actuallyoccurs and the combustion reaction takes place. Traditionally, theprimary air shutter has been located at a point upstream from the pointof fuel introduction. Thus, the flow of cold primary air must pass bythe orifice and, as a result, strips heat away from the orifice. Theorifice is prone to freezing due to the varying composition/watercontent of the fuel being used in conjunction with the pressure dropthat occurs at this point. In order to change the capacity of the mixer,the orifice needs to change in size and/or the pressure adjusted. Thistypically involves the dismantlement of the mixer assembly to provideaccess to the orifice.

SUMMARY OF THE INVENTION

The object of this invention is to prevail over the drawbacks relatingto prior art in this field as stated above.

The primary air intake has been relocated to a position downstream ofthe fuel gas point of introduction. Now the stream of fuel leaving theorifice is at its highest velocity, and thus, lowest pressure, at thepoint of air induction rather than the traditional upstream location.This design allows for a greater volume of air to be introduced than ona similarly sized traditional mixer.

A removable orifice holder has been designed to allow for the removal ofonly the holder to access the orifice for maintenance and set-up. Thisallows the rest of the assembly to remain stationary as it is notrequired to be removed from the combustion chamber.

A port has been positioned adjacent to the orifice location to allow theuse of an orifice preheat line to be installed. This port provides apoint of entrance for the high temperature, products of combustion (POC)from the mixing chamber into the mixer housing. These POC can be drawnback and directly across the orifice, using the same physics principleas previously discussed, to further prevent the freeze off issuestraditionally encountered.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded view of the mixer assembly with an optionalventuri barrel

FIG. 2 is a view of all components assembled to form complete mixer

DETAILED DESCRIPTION OF INVENTION

With reference to FIGS. 1-2 the mixer component orientation andconstruction can be explained.

FIG. 2 shows the location of the fuel inlet 1 to the mixer.

As shown in FIG. 1 the mixer is comprised of three mandatory separatecomponents with an optional component that will assist in the mixing ofthe fuel if required. The main mixer body 3 contains the port for thepreheating of the orifice 4 by utilizing the high temperature POC aswell as the port for the orifice holder 1. A portion of the main body 3has a reduced diameter and four rectangular holes removed from the stockat 90 degrees in an array around the outside diameter. The reduction ofdiameter allows for the primary air shutter 5 to slide over top of themixer body 3. The reduced diameter portion of the mixer body 3 and theprimary air shutter are of the same length. This is the base for theprimary air shutter 5 which also has the same dimensioned four holesremoved at a 45 degree offset from the mixer body 3 holes. This allowsfor the primary air to be adjusted within the completely open andcompletely closed positions of the shutter. The mixing shutter 5 has thesame outside diameter as the mixer body 3 and an internal diameterslightly larger than the outer diameter of the reduced section of themixer body 3. This allows for the primary air shutter 5 to rotate freelyabout the center line axis of the mixer. FIG. 2 shows the set screw hole2 that allows for the primary air shutter to be secured in the desiredposition and also constrains the degrees of rotation between thecompletely open and completely closed position of the primary airshutter (3, FIG. 1.). The optional venturi barrel 6 is shown in FIG. 1and is used to aide in mixing of the air/fuel before the nozzle. FIG. 1shows the orifice 2 threaded into the orifice holder 1 and is threadedinto the port 7 located at the back of the mixer body 3. It is thisconfiguration that allows the orifice holder to be removed from theassembly allowing maintenance or set-up to easily be performed on theorifice without the need to remove the entire mixer assembly from thecombustion chamber.

With reference to FIG. 1, as the fuel passes through the orifice 2, thehigh velocity gas creates a low pressure area at the primary air shutter5 thus, inducing air into the mixer body 3. The primary air shutter 3 isrotated to adjust the amount of air entering the mixer, based on therequired amount of air needed to attain the desired combustion reaction.

A line, such as a piece of stainless steel tubing, may be connectedbetween the orifice preheat port 4 and the flame front where the POC areproduced. As the high velocity fuel enters the mixer, the low pressurecreated draws high temperature POC down and across the adjacent orifice,effectively heating the orifice well above the temperature at which icewill form.

1. The relocation of the primary air introduction being downstream ofthe orifice will prevent heat loss from the orifice due to very coldcombustion air passing over and striping valuable heat from the orifice.2. The relocation of the orifice preheat port, to a position directlyadjacent to the orifice, draws high temperature POC directly down andacross the orifice which heats the orifice preventing the build-up andaccumulation of ice, thus, preventing freeze-off of the orifice.
 3. Aremovable orifice holder that allows the user to perform maintenance orset-up on the orifice without dismantling the assembly and removing itfrom the combustion chamber.